The present invention relates to stable materials having enhanced extensibility and a mechanical post-processing method for making the same. High extension materials, such as nonwoven webs and film webs are particularly well suited for use in disposable absorbent articles such as diapers, incontinence briefs, training pants, feminine hygiene garments, and the like, as they are able to be used in portions of the article where high extensibility can aid in the article""s fit to the body.
Nonwoven webs may be manufactured into products and components of products so inexpensively that the product may be viewed as disposable after only one or a few uses. Representatives of such products include diapers, training pants, wipes, garments, incontinence briefs, feminine hygiene garments and the like.
Nonwoven webs may be treated to provide the nonwoven web with certain properties. For example, U.S. Pat. No. 5,244,482 issued to Hassenboehler, Jr. et al. on Sep. 14, 1993 discloses a method for treating a nonwoven web wherein the nonwoven web is heated at an elevated temperature and uniaxially drawn to consolidate and stabilize the nonwoven web. Such nonwoven webs are noted to exhibit an increased elasticity after processing. Such elasticity increase is recognized as being caused by the new xe2x80x9cmemoryxe2x80x9d instilled by the heating of the nonwoven web. For applications desiring enhanced extensibility rather than elasticity, such heating is therefore not desirable. Additionally, such drawing and setting of the nonwoven web by heating at an elevated temperature often causes fiber embrittlement and the nonwoven web to exhibit increased gloss. For many applications involving skin contact, e.g., such as in diaper coverstock, such attributes are contrary to the desired cloth-like properties of softness and non-plastic, (low gloss) appearance. Lastly, the requirement of heating the nonwoven web to consolidate and stabilize the web adds to the complexity and cost of the process.
U.S. Pat. No. 4,981,747 issued to Morman on Jan. 1, 1991, discloses a xe2x80x9creversibly neckedxe2x80x9d material. It is taught that the unstabilized necked material must be held under high tension on the re-wound roll until such time as the further heat setting step is performed to stabilize the material. Such a material will again suffer the deficits noted above with respect to preferred skin contact applications, and will enhance the elastic properties of the material rather than the extensible behavior of the material.
U.S. Pat. No. 5,226,992 issued to Morman on Jul. 13, 1993, discloses a method of producing a composite elastic necked-bonded material. A tensioning force is applied to at least one neckable material, such as a neckable nonwoven web, to neck or consolidate the material. Instead of heating the consolidated nonwoven web, this patent teaches superposing the tensioned consolidated nonwoven web on an elastic material and joining the tensioned consolidated nonwoven web to the elastic material while the tensioned consolidated nonwoven web is in a tensioned condition. By joining the tensioned consolidated nonwoven web to the elastic material while still in a tensioned condition, the nonwoven web is constrained to its necked dimension. Such a procedure does not provide a means for producing a stabilized extensible web without the attachment of the nonwoven web to an additional elastic layer.
It is an object of the present invention to provide a stabilized extensible necked nonwoven web, capable of being wound into stable rollstock or festooned form, suitable for subsequent conversion or combining operations.
It is also an object of the present invention to provide a stabilized extensible necked nonwoven web, capable of very high speed extension via mechanical straining means.
It is also an object of the present invention to provide a post-processing method for producing a stabilized extensible necked nonwoven web.
It is also an object of the present invention to provide a post-processing method for producing a stabilized extensible necked nonwoven web that does not require heating of the neckable material to elevated temperatures, to enhance the extensible properties rather than the elastic properties and to substantially preserve the original properties of the neckable nonwoven web.
As used herein, the term xe2x80x9celasticxe2x80x9d, refers to any material which, upon application of a biasing force, is stretchable, that is, elongatable, to at least about 60 percent (i.e., to a stretched, biased length which is at least about 160 percent of its relaxed unbiased length), and which, will recover at least 55 percent of its elongation upon release of the stretching, elongation force.
As used herein, the term xe2x80x9cextensiblexe2x80x9d refers to any material which, upon application of a biasing force, is stretchable, that is, elongatable, to at least about 60 percent without suffering catastrophic failure (i.e., to a stretched, biased length which is at least about 160 percent of its relaxed unbiased length), but does not recover more than 55 percent of its elongation upon release of the stretching, elongation force.
As used herein, the term xe2x80x9chighly extensiblexe2x80x9d refers to any material which, upon application of a biasing force, is stretchable, that is, elongatable, to at least about 100 percent without suffering catastrophic failure (i.e., to a stretched, biased length which is at least about 200 percent of its relaxed unbiased length), but does not recover more than 55 percent of its elongation upon release of the stretching, elongation force.
As used herein, the term xe2x80x9cstabilizedxe2x80x9d refers to a material of the present invention which is capable of being stored in a stable condition in any common or conventional web storage manner without the need for further heating or the addition of or joinder with other webs to stabilize the material. Such storage means would include for example, low tension rolls or festooned material in boxes.
As used herein, the term xe2x80x9cnonwoven webxe2x80x9d, refers to a web that has a structure of individual fibers or threads which are interlaid, but not in any regular repeating manner. Nonwoven webs have been, in the past, formed by a variety of processes such as, for example, meltblowing processes, spunbonding process, and bonded carded web processes.
As used herein, the term xe2x80x9cnecked materialxe2x80x9d, refers to any material which has been constricted in at least one dimension by applying a tensioning force in a direction that is perpendicular to the desired direction of neck-down.
As used herein, the term xe2x80x9cneckable materialxe2x80x9d, refers to any material which can be necked.
As used herein, the term xe2x80x9cpercent neckdownxe2x80x9d, refers to the ratio determined by measuring the difference between the un-necked dimension and the stabilized necked dimensions of the neckable material in the direction of necking, and then dividing that difference by the un-necked dimension of the neckable material, then multiplying by 100.
As used herein, the term xe2x80x9ccomposite elastic materialxe2x80x9d, refers to a material comprising an elastic member joined to a stabilized extensible necked material. The elastic member may be joined to the stabilized extensible necked material at intermittent points or may be continuously bonded thereto. The joining is accomplished while the elastic member and the stabilized extensible necked material are in juxtaposed configuration. The composite elastic material is elastic in a direction generally parallel to the direction of neckdown of the stabilized extensible necked material and may be stretched in that direction to the breaking point of the stabilized extensible necked material. A composite elastic material may include more than two layers.
As used herein, the term xe2x80x9cpolymerxe2x80x9d, generally includes, but is not limited to, homopolymers, copolymers, such as, for example, block, graft, random, and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term xe2x80x9cpolymerxe2x80x9d shall include all possible molecular geometric configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic and random symmetries.
In accordance with the present invention there is provided a method of producing a stabilized extensible necked material comprising the steps of:
providing a neckable material;
applying a tensioning force to the neckable material to neck the material; and
subjecting the necked material to mechanical stabilization to provide a stabilized extensible necked material. The stabilized extensible necked material is easily extended in a direction parallel to the direction of necking. A preferred method for mechanically stabilizing the necked material comprises subjecting the necked material to incremental stretching in a direction generally perpendicular to the necked direction.
The method may also comprise the additional step of winding the stabilized extensible necked material onto a take-up roll or festooning the stabilized extensible necked material into box.
The method may also comprise the additional step of joining the stabilized extensible necked material to an elastic member to form a composite elastic material.
If the material is stretchable it may be necked by stretching in a direction generally perpendicular to the desired direction of neck-down. The neckable material may be any material that can be necked sufficiently at room temperature. Such neckable materials include knitted and loosely woven fabrics, bonded carded nonwoven webs, spunbonded nonwoven webs, or meltblown nonwoven webs. The neckable material may also have multiple layers such as, for example, multiple spunbonded layers and/or multiple meltblown layers or film layers. The neckable material may be made of polymers such as for example, polyolefins. Exemplary polyolefins include polypropylene, polyethylene, ethylene copolymers, propylene copolymers and blends thereof. The neckable material may be a nonelastic material such as for example a nonelastic nonwoven material.